VoNR Isn’t Just VoLTE on 5G — Here’s What Most People Miss

This episode is based on a technical conversation between Me and Tech Explorer 📶, drawn from real-world experience with 5G SA deployments and IMS voice migration.

Tech Explorer 📶:Mohamed, I thought VoNR is just voice over 5G — like VoLTE but faster.
Isn’t it the same IMS, just riding on a new access?

Me (Mohamed):That’s a common assumption — but it’s not that simple.

Yes, VoNR and VoLTE both use IMS, but the underlying architecture, timing, and design trade-offs are different — and those differences matter a lot in real deployments.

I learned this firsthand when helping an operator migrate from NSA VoLTE fallback to true VoNR over SA.

📡 What VoNR really is:

VoNR (Voice over New Radio) means end-to-end voice over a 5G SA network, without falling back to 4G.

It uses:

• 5G RAN (gNB)
• 5G Core (5GC)
• IMS Core (same as VoLTE, but tighter integration needed)
• And importantly: IMS registration and QoS flows managed by 5GC

Tech Explorer 📶:
So why is deploying VoNR tricky?

Me (Mohamed): Here’s what makes VoNR challenging in practice:

1. SA coverage must be dense and reliable
   → Unlike NSA, you can’t fall back to LTE. Any 5G coverage hole kills the call.
2. End-to-end latency must be under tight bounds
   → We target ~20ms one-way latency for HD voice.
   → This means optimizing the transport, radio scheduler, and IMS timers.
3. SDP negotiation is tighter
   → 5G devices often support both EVS and AMR-WB — but require careful codec configuration for quality and fallback.
4. 5GC and IMS coordination is crucial
   → SMF must anchor correct QoS flows for voice (QFI, 5QI = 1)
   → N2 and N5 interfaces must sync up for seamless call setup

In one project, I saw dropped VoNR calls due to misconfigured P-CSCF discovery — the UE couldn’t reach the IMS server through the right PDU session.
We fixed it by enabling UE route selection policy (URSP) — and VoNR started flowing like a charm.

Tech Explorer 📶: What about handovers? Can I move from VoNR to VoLTE if needed?

Me (Mohamed):
Yes — that’s called EPS fallback or RAT fallback, but only if the operator supports both EPC and 5GC in parallel.

However, true VoNR deployments try to avoid fallback altogether.
That’s why most operators only activate VoNR in SA zones with solid QoS assurance.

And don’t forget:

• You need IMS centralization across both 4G and 5G
• Devices must support dual IMS registration and SRVCC logic, even if not used frequently

💡 Summary: VoNR ≠ VoLTE on 5G

Tech Explorer 📶:
So what should operators focus on when deploying VoNR?

Me (Mohamed):
✅ Optimize 5G coverage and latency before turning on VoNR
✅ Ensure IMS registration flows are validated in 5GC
✅ Test URSP policies, N26 interface fallback, and codec fallback
✅ Train the team — VoNR isn’t a copy-paste from VoLTE

We’ve seen that when VoNR is deployed well, call setup time drops below 1s, and HD voice is significantly improved compared to legacy networks.

🎓 Check below our Voice over 5G recorded course to learn more about the technology